The present invention relates to amplifiers, and more particularly to sense amplifiers that sense the impedance between two terminals.
Sense amplifiers that sense the impedance between two terminals are widely used in electronic devices. For example, in programmable logic devices (PLDs), an output signal based on whether or not a programmable cell has been programmed to a conductive state is derived from a sense amplifier which senses the impedance between cell terminals.
In a typical sense amplifier sensing the impedance between two terminals, the two terminals are connected to two different voltages so that the voltage on one or both of the terminals depends on the impedance between the two terminals. The voltage that depends on the impedance is connected to an input of an amplification stage that provides a high voltage swing on the amplifier output.
In many amplifiers, in order to obtain a high switching speed, the voltage on the input of the amplification stage is kept close to the stage trip voltage (i.e., threshold voltage). This, however, may lead to a high power consumption in the amplification stage if, for example, the amplification stage is implemented using CMOS technology. Further, the power supply voltage variations and processing variations can cause the voltages on the input of the amplification stage to converge to the stage trip voltage reducing the sense amplifier noise margin below an acceptable value.
Thus, it is desirable to provide a sense amplifier which combines a high speed with a low power consumption and which is more tolerant to supply voltage variations and processing variations.